The present invention relates to an improvement in the methods used to separate desired minerals from the naturally occurring ore in which they are found. More specifically, to a method of separating these minerals which does not require the addition of chemical agents to the process in order to stimulate separation reactions, many of which are harmful to the environment and all of which add unnecessary cost to the production of these minerals.
In the past, miners and mining companies have struggled to find and perfect a method of separating desired minerals, most commonly precious metals such as gold and silver, from the body of the ore with which they are associated. These recovery problems are compounded due to the fact that these ores are refractory in nature, that is to say that they do not respond well to the heating and melting techniques that are employed with other types of ores.
The refractory nature of these ores is a result of two different possible chemical compositions contained therein. The first of these is the presence of sulfide minerals within the ore that are chemically associated with the precious metal. This association is difficult to break and requires that the sulfides be decomposed prior to the recovery. The decomposition of the sulfides is usually accomplished by pressure oxidizing the ore at highly elevated temperatures and pressures and under acidic conditions which will oxidize the sulfides and make the precious metal much easier to recover.
The second circumstance that will cause an ore to react in a refractory manner is the presence of organic carbon within its chemical structure. This creates a problem because of the method that is used to recover the precious metal contained in the ore. The recovery is most commonly accomplished by the introduction of cyanide into the ore which leaches out the precious metal and forms a cyanide complex containing the metal and the cyanide. This cyanide complex can then be absorbed by activated carbon from which the precious metal is later recovered. The presence of organic carbon in the ore is a problem because it will compete in the precious metal absorption process with the supplied activated carbon. This works to rob precious metal from the recovery process which limits its effectiveness.
This condition is not responsive to the cyanide method that is effective with sulfides and so requires the application of a different process to the ore to recover the precious metal. This is commonly accomplished by subjecting the ore to a chlorine containing compound prior to the recovery process. The addition of chlorine does solve the organic carbon problem but is not effective when the ore is also refractory due to the presence of sulfides and is also very expensive due to the added cost of the chlorine and the necessary additional steps needed to process the byproducts.
The prior art has attempted to address these problems by providing a single step method of dealing with refractory problems due to both the presence of sulfides and organic carbon. Most notably, in U.S. Pat. No. 5,536,480 issued to Simmons, a precious metal recovery method is disclosed in which a pressurized oxidation mechanism is employed to treat ores that are refractory due to the presence of organic carbon. This process is claimed to reduce the ability of the organic carbon to rob the precious metal from the recovery process and to also substantially oxidize any sulfides contained in the ore. However, this process requires the creation of a highly pressurized and oxidized environment which greatly increases the costs involved in the recovery of precious metal from refractory ores.
From the forgoing discussion it can be seen that it would be advantageous to provide a method of recovering precious metals such as gold and silver from common and refractory ores. Additionally, that it would be advantageous to provide such a method that would be in a single step as effective in precious metal recovery from ores that are refractory due to the presence of sulfides as with ores that are refractory due to the presence of organic carbon. Further, to provide such a method that does not require the addition of chemical agents or a highly pressurized environment to accomplish the recovery of precious metals from ores.
It is the primary objective of the present invention to provide a method of initiating the process of removing the values from wastes such as ore or mine tailings typically obtained from or stored around mine sites.
It is an additional objective of the present invention to provide such a method of material separation which does not require the use of additional chemicals to the ore or mine tailings to initiate this separation process.
It is a further objective of the present invention to provide such a method of mineral separation that is less expensive, simpler and more effective to operate than present methods.
It is a still further object of the present invention to provide such a method of mineral separation that produces the desired results in shorter periods of time then those that are currently available and that requires little maintenance during normal operation.
These objectives are accomplished by the use of an ore separation operation that begins with a conveyor system which feeds the ore into a specially designed primary grinding mill. The primary grinding mill grinds the ore into a very fine powder, at least half of which is 100 mesh (0.0059xe2x80x3 or 0.150 mm) or smaller. This powder is then blown by the primary grinding mill through a discharge duct and into a primary sizing baghouse which separates the smaller particles (100 mesh or smaller) from the larger oversize particles. The oversized particles are channeled from this point through an oversized duct to the secondary grinding mill where they are ground again and blown to the secondary sizing baghouse. The smaller particles go to the final ore sizing baghouse and the oversize ore particles are sent back to the storage silo to go through the ore grinding process again. The grinding process is repeated until all the ore is the proper size.
Once the ore has been ground to the proper size (whether in the primary or secondary grinding mill), it is channeled into the final ore sizing baghouse where the ore particles are separated from the air stream and sent to the blower mill which, in turn, blows them into the air mixing chamber of the ore-roasting oven. In the air mixing chamber, the ore powder is mixed with a precise amount of air (the exact amount being determined by the chemical properties of the ore being processed) and then blown into the ore-roasting oven. Within the ore-roasting oven, the ore is flash heated to a temperature that exceeds 300 degrees Fahrenheit which ignites the powdered ore mixture and some of the combustible chemicals contained in the ore. This ignition process initiates a pyrolysis reaction with the other chemicals in the ore and begins the separation process that is the primary function of the invention.
When these processes are completed, the roasted ore particles are channeled into a primary quench chamber where they are quickly cooled with a water spray. At this point, the extremely fast changes in the ore particles"" temperature coalesces and cracks them, which separates the mineral or minerals from the remainder of the undesirable material contained therein. Once these processes are complete, all but the very smallest of the ore particles drop to the bottom of the primary quench chamber where they, and the cooling water, are removed by a slurry pump to the ore concentration units which separate the values from the wastes. The lightest of the particles in the primary quench chamber are transferred to the secondary quench chamber where they undergo a sequence of processes and reactions that are very similar to those that occur within the primary quench chamber.
Finally, after being separated from the ore, both the ore and water that are used in the separation process are transferred to cleaning units contained within the body of the invention and are purified before either their release into the environment or prior to their being recycled for further use. These processes ensure that the use of the present invention conforms to all Environmental Protection Agency and all other governmental regulations, and that the use of the invention will have the least possible degree of detrimental impact upon the natural environment.
For a better understanding of the present invention, reference should be made to the drawings and the description in which there are illustrated and described preferred embodiments of the present invention.